This invention relates to electric heating elements used to heat a tobacco flavor medium in an electrical smoking article. In particular this invention relates to such a heating element arranged in a radial array.
One type of electrical smoking article is disclosed in copending, commonly-assigned U.S. patent application Ser. No. 07/444,746, filed Dec. 1, 1989 and now U.S. Pat. No. 5,060,671, which is hereby incorporated by reference in its entirety. In such an electrical smoking article, a flavor bed of a tobacco flavor medium, such as tobacco or tobacco-derived substances, is heated electrically to release a tobacco flavor substance without burning. As the tobacco flavor medium is heated, a smoker at the mouth or downstream end of the device draws air in and around the heating element by inhaling, and thereby receives the tobacco flavor substance.
The above-identified application discloses as a possible heater configuration a non-reactive radial array of blades upon which the tobacco flavor medium is dispersed, providing a number of flavor puffs equal to the number of blades. In one embodiment the blades in the radial array are generally U-shaped but with rectangular inner and outer corners. Current flows through such rectangular U-shaped or slotted blades between the two connector points around the slotted area. Current density in such a blade is non-uniform, peaking at the sharp inner corners at the end of the slot. High current density leads to areas of extreme heating around the inner corners, with temperatures in excess of the desired operating temperature.
It would be desirable to provide a heating element with a current density profile which would maximize the distribution of heat so as to provide heat to the greatest amount of tobacco flavor medium.
It would also be desirable to provide a heating element which is a radial array of generally U-shaped blades which would have only rounded corners to eliminate areas of heating, or "hot spots", which exceed the desired operating temperature.
It would also be desirable to provide a heating element with optimized three-dimensional variations in the geometric configuration of the element in order to reduce the area in which heating exceeds the desired operating temperature by improving current distribution across the heating element.
It would also be desirable to provide a heating element comprised of a material which optimally minimizes mass so as to lower energy consumption while providing the necessary strength characteristics for use in the desired dimensions.
Furthermore, it would be desirable to provide a heater which would have dimensions enabling it to fit inside an electrical smoking article which is approximately the size and shape of a conventional cigarette.
It would further be desirable to provide a heater made from a material which evolves no undesirable components when heated.
Finally, it would be desirable to produce a heater with one piece construction which could be produced by machining or molding processes, or by extruding and machining processes, which are sufficiently cost-effective to allow the heater to be a replaceable and disposable component.